The invention concerns a rheometer comprising an upper measuring part and a lower measuring part, between which a measuring chamber is formed for receiving a sample of a substance to be examined, wherein the two measuring parts can be moved relative to each other and, in particular, be turned or pivoted, and with a heating device for heating at least the lower measuring part.
A rheometer for determining the characteristic rheological values of a viscous substance usually comprises a lower stationary measuring part (stator) and an upper measuring part (rotor) which can be axially adjusted, rotated, or pivoted and between which a measuring chamber is formed to receive a sample of the substance to be examined. The forces and tensions produced through relative motion between the upper and lower measuring parts are measured and can be used to calculate the desired characteristic rheological values. The characteristic rheological values depend i.a. on the temperature of the sample during the measurement. To obtain reproducible characteristic rheological values, one therefore tries to heat the sample to a predetermined temperature and keep it at this temperature throughout the entire measurement. To obtain exact measured data, it is thereby necessary that the temperature is homogeneously distributed within the sample of the substance to be examined. This is not the case in many heating devices of conventional structure.
In many cases, a heat exchanger in the form of a plate is used as a heating device which is penetrated by channels in which warm fluid flows. Since the channels in the plate have a mutual separation, the plate does not heat uniformly in all regions thereby making it more difficult to obtain homogeneous temperature distribution in the sample of the substance to be examined.
Moreover, it is sometimes desirable to observe the sample during measurement using a video camera for detecting and evaluating the particle distribution within the sample. Towards this end, a small gap is conventionally left in the plate of the heat exchanger and the sample is observed through this gap. The gap may disadvantageously prevent a homogeneous temperature distribution in the sample with the inhomogeneity, moreover, occurring exactly at the location of observation or measurement, thereby disadvantageously influencing the accuracy of the measured result.
It is the underlying purpose of the present invention to produce a rheometer of the above-mentioned type, with which the lower measuring part can be heated with a homogeneous temperature distribution.